What is causing trapped ions to heat up? In an ion trap, electrodes (shown here in gold) produce electric fields that confine the ion (green sphere) to a small volume. Randomly fluctuating dipoles on the surface of these electrodes generate electric field noise. The dipoles form when single atoms adsorb on the metal surface. Vibrations (phonons) in the metal cause the dipoles (purple arrows) to fluctuate. Ions trapped in the vicinity of the metal surface sense these electric field changes and heat up.